46mm vs 48mm throttles

[jimmy p.]

Gruppe,
Has anyone actually real world A-B'd, or quantified in any way the maximum amount of HP that can be made on 46mm Throttles?

I know the 48s came on the Evo 2 and Evo 3 engines,,, but I think we all know that was for homologation, not necessity to make the 220 or 238 hp. Current cars are easily exceeding that on 46s.

For example, my BTCC car makes 270HP on 46mm throttles, the early Grp A engines which were making over 300 HP before the 48s were homolgated.

Wondering if anyone has done the dyno or flow bench research to see when a 46mm throttle starts to be the restricting factor in engine performance.

Cheers
jimmy p

[Larsen-Racing]

Don't think Evo2 had 48mm TB's though, but 1990 215hp model did have 48mm.

[jimmy p.]

Hmmm,,, I thought they did,,, but maybe not.
I thought the 48 was homologated in the Evo 2,,, you would think I'd know this stuff by heart...
In any case, question is still as stated.

[pmartins]

EVO2 are 48mm on the head side and 46mm on the air intake.

discussion between 48 and 46 http://www.s14.net/forums/showthread...ight=48mm+evo2

these are the ones that i know....

street cars:

1)195hp/200hp/320is = 46mm ones

2)220hp(EVO2) = 46mm on the air intake side and 48mm to the head side-these ones also have different intake trumpets

3) 215hp incl. Cecottos+238 hp EVO3 = 48mm ones
never have seen any differences between 215hp and EVO3 ones

race cars:

i think there are 8-10 different sliders available---
48mm ones for straight fitted engines and engines in 30 degrees position....
the same was available in 49,5mm
also in different lenght i have seen some....

how much different Gr.A TBs are available i don't know....

Markus

[jimmy p.]

Ok,,, just to keep this thread on topic, its not a dissertation of the different throttle body types and applications.
This thread soley is on power output.

Understanding what the power plateau is with stock throttles and if anyone has ever researched it or quantified it.

Where do stock 46mm road throttles become the limiting factor of a modified S14?

Say for example (crude example) if you were to plop a set of 46mm street throttles on a late 360 HP DTM engine,,, how much power could we assume it would make?

Has anyone ever A - B'd a set of throttles and seen the outcome or what the cutoff is where the 46 mm throttle becomes the restrictive element?

Cheers
jimmy

[Hoofty]

I did some fag-packet calculations on excel but it won't let me upload the file. At any rate, going to 48s isn't required for out and out air flow. Assuming a relatively racey volumetric efficiency (110%) and a 7500rpm limit, the intake speed through the throttle bodies won't top 35m/s with 46s, and is about 10% lower than that for a set of 48s. The normal limit for a restricted race engine is sonic flow through the restrictor (343m/s) but those engines are much bigger and the restrictors are about 30% as large as the S14 TBs. At about 10% of sonic flow it can't be anything to do with that. You'd have to make an S14 spin at about 100,000rpm to run into that hurdle.

Some quick research from Jenvey (a UK TB manufacturer) seems to back this up:

It helps to understand the relationship between size and output to consider that a 2L Formula 3 engine produces 200+BHP through a 26mm (531 sq mm) restrictor, whilst, say, a 75mm throttle body is eight times larger at 4,418 sq mm! Similarly, in an experiment to curb the power of 270 BHP touring car engines, we reduced the size of the single throttle body to less than 44mm (1520 sq mm) before there was any noticeable reduction: a 75mm body has three times the flow.

My guess would be that the 48s provide some increase in volumetric efficiency at race rpm, but then I'm not an engine designer. And would I swap mine back? No way, look at those spindles!

Nick

[jimmy p.]

Thanks Nick,
Thats exactly the pointy headed discourse I was looking for.
I know there are many factors, but thats what I am trying to determine (and get into a thread for all eternity),,, at what point does the 46mm throttle become your limiter to making power, and then its necessary to upgrade to 48s.

I am in this boat now, and for all the stuff we write about these cars and these engines, I cant find anywhere that has those actual facts backed up by anything.

I think everyone assumes you must go to 48s, but I cant find anywhere that says when and why and how much.

[Ironhead]

These are good questions....

As I am sure you know, Gustave did back to back dyno comparisons on the same engine, swapping 46 and 48 throttles, but that does not really answer your question.... The engine was the standard 2.5 with 11.25 compression and 284/276 cams. It made measureably more power with the 48s....even measurably more IIRC with the 48 TBs than with 46 TBs ported to 48.

The problem is, to really come up with an answer, the testing would have to be done on a no holds barred, cost no object race engine with 3xx motorsport cams and all the goodies. Someone who has forked over the dough for such an engine probably isn't going to much care what can be done with 46mm throttles....

But if any given mildly modified engine will make more power with 48s than with 46s, whatever the specific quantifiable facts are, the question becomes less relevant doesn't it? My question would not be how much power can be made with 46s, but rather how large can throttles become before it is too much?

At some point, and I know you are trying to discern what point, the 46 throttles become like restrictor plates. With a high dollar investment, engines can be designed to make surprisingly large power with surprisingly small restrictor plates in order to meet the rules.

But, like you, I would certainly like to know the answer...

[Hoofty]

I realise that the 'some increase in volumetric efficiency' comment is about as useful as saying it 'gives it more power', but with my limited/non-existant experience of physically tuning engines it's the best I could think up (I think it's correct, but not very revealing). Peak VE should (I believe) coincide with the peak of the torque curve - what point does that occur on a Gp.A spec engine? I'd assume much, much higher than the stock 4750rpm. Another point is that intake pulse tuning depends only on length of the runner, not the diameter - shouldn't be that then.

[jimmy p.]

Ironhead,
I forgot about Gustave's test, I'll see if I can dig that up.
I would assume that would have been with an AFM?
I dont think Gustave ever reached operation with his 2.5 on Alpha N did he? Cant remember.

I too would also like to know the flip side as you asked,,, if 46 is the bottom,,,, how much power can you make with 46s,,, where is the other side to that.
I guess thats one that will top out at 50, because thats the biggest hardware we have to offer from the E34 throttles unless someone makes something custom.

After this thread sits for a weekend or so I guess we will see if anyone knows (well and if they know if they will post it).

Cheers
jimmy

[m3pat2]

Jimmy, I don't have any scientific data in regards to the horsepower side of things. But I do have some feedback regarding how fast the engine is able to increase rpm between 46mm and 50mm TBs. I didn't know if this is something that would deviate too far from what you're looking for.

For my engine specs (See upper right - user name header)
46mm seem to pull very smoothly with a steady rpm increase up to around 6,800 rpm. after that the rate of rpm increase seems to flatten out.

50mm E34 M5 TB seems to loose a lot of torque before 5,000 rpm. After that though the rpms increase at a very fast rate. I was only able to get up to 7,800 rpm before other issues, I personally believe 50's will feed an engine up to 9,000rpm easily...and possibly more.

Obviously the more rpms you can generate the more HP. So let's hypothetically say 46mm start limiting power at 8,000 rpm, 48mm at 9,000 rpm and 50mm at 10,000 rpm. To even test this out we would need a race spec. engine and a couple of people to bring in various TB sizes. Also it seems that John is running 49.5mm another size that would be nice to test.

It sounds like you're not running 48's on any of your cars, maybe someone near you could bring in some 48mm to do a back to back with the 46's?

[Ironhead]

Ironhead,
I forgot about Gustave's test, I'll see if I can dig that up.
I would assume that would have been with an AFM?
I dont think Gustave ever reached operation with his 2.5 on Alpha N did he? Cant remember.

I too would also like to know the flip side as you asked,,, if 46 is the bottom,,,, how much power can you make with 46s,,, where is the other side to that.
I guess thats one that will top out at 50, because thats the biggest hardware we have to offer from the E34 throttles unless someone makes something custom.

After this thread sits for a weekend or so I guess we will see if anyone knows (well and if they know if they will post it).

Cheers
jimmy

I am pretty sure Gustave was still using an AFM when he did the test.

Although some will pretend they have all the answers (John?), I don't think anyone will be able to quantify this one for us.
There are probably remnants from the E30M3 DTM engine team from BMW Motorsport who would know the answer, or have a very good approximation. I have no idea how you would tap their brains though, assuming they even remember.

Funny isn't it? An engine that has been raced as much as the S14, and there are still so many questions.....

[Az in Oz]

Jimmy, I like where you are going with this. I started a thread a while back trying to find out what horsepower the different year Grp A cars were putting out and how the engine specs changed from 1987 to 1992..... with very little response. I hope you have more luck.
I'm with Ironhead on this.....Funny isn't it? An engine that has been raced as much as the S14, and there are still so many questions.....

FWIW I'll most likely be rebuilding my engine in a year or so and a mate has a set of 48's that I will most likely bolt on and do a dyno run with but I'm not going to upgrade my 46's. This isn't of much use to you know though I know.

Good luck
Aaron

[Anders]

I'm in Sweden right now, and I've seen some really nice engines. Although it's not "apples to apples" because it's turbocharged, one guy is putting out 880 hp using 46mm TBs.

[Jake]

I think the main problem with finding answers to questions like this is that it takes a considerable investment to quantify. An investment like this isn't usually made just so someone can post up the results in public. It's not too far fetched to assume all the info anybody ever wanted to know is out there, somewhere, but it just isn't made available.

What's needed is a group of people to share the expense of finding out these answers. But would people really donate to such a cause?

Jake